1. Field of the Invention
Embodiments of the present invention relate to an inkjet head and a recording device including the inkjet head. Specifically, the inkjet head causes pressure fluctuation to be generated in individual liquid chambers, and thereby the inkjet head sprays liquid from infinitesimal nozzles formed in the corresponding individual liquid chambers.
2. Description of the Related Art
An inkjet head and a recording device including the inkjet head have conventionally been known such that the inkjet head causes pressure fluctuation to be generated in individual chambers, and thereby the inkjet head sprays liquid from infinitesimal nozzles formed in the individual chambers. As a method for generating the pressure fluctuation in the individual liquid chambers of the inkjet head, many methods have already been realized and implemented in products.
For example, the thermal inkjet method and a method using an actuator can be considered. In the thermal inkjet method, liquid is vaporized by disposing a heater in the individual liquid chamber, and the pressure fluctuation caused by the vaporization is utilized. In the method using the actuator, the actuator is disposed in the individual liquid chamber. The method using the actuator can further be classified depending on the type of the actuator. For example, a piezoelectric element method and an electrostatic method have been known.
In the method using the actuator, various types of ink corresponding to various physical properties can be utilized. On the other hand, for the method using the actuator, high densification of the arrangement of the liquid chambers and downsizing of the head have been difficult. However, a technique of high densification is being established. In the technique, a so called “Micro Electro Mechanical Systems (MEMS)” process is utilized.
For example, the high densification can be realized by laminating an oscillation plate, an electrode, and a piezoelectric material on the individual liquid chamber by using the thin-film forming technology, and by patterning an individual piezoelectric element and wirings by using a semiconductor device manufacturing process (photolithography). For example, Patent Document 1 (Japanese Patent Laid-Open Application No. 2005-144847) discloses a technique for patterning a wiring layer.
Further, when a piezoelectric element formed by a thin film process is utilized, since the oscillation plate has a thin film structure having a thickness of several micro meters, the oscillation plate tends to be deformed by a residual stress due to the lamination of the piezoelectric elements. Further, since a thickness of a substrate that forms a fluid channel is small, it is preferable that sufficient stiffness be ensured and processing accuracy during a manufacturing process be improved. As a countermeasure for these problems, Patent Document 2 (Japanese Patent Laid-Open Application No. 2004-082623) and Patent Document 3 (Japanese Patent Laid-Open Application No. H11-291497) disclose a method in which a supporting substrate is utilized. In the method, end portions of the oscillation plate are reinforced by joining the piezoelectric elements with the supporting substrate, while disposing partition walls between the piezoelectric elements. Thereby the stiffness of the fluid channel substrate is improved. Namely, the crosstalk that accompanies the high densification of the arrangement of the liquid chambers can be reduced, and at the same time, handling in the manufacturing process can be improved. Thereby mass productivity is improved.
For a structure where the supporting substrate is joined with the fluid channel substrate, individual electrodes and a common electrode that are extended from an upper electrode and a lower electrode by patterning of the wiring layer may be required to be extended outside a joining area where the supporting substrate is joined with the fluid channel substrate, so that the individual electrodes and the common electrode are connected to a driving circuit. In order to improve reliability of the bonding between the supporting substrate and the fluid channel substrate, the height of the joining area may be adjusted to be equal to that of the layer structure.
In Patent Document 1, the effect of the positional shift of the supporting substrate on the liquid discharging property is mitigated by making the width of the partition wall of the supporting substrate smaller than the width of the piezoelectric body formed on the partition wall of the fluid channel or the width of the laminated film including the upper electrode. However, the layer structure of the partition wall portion of the supporting substrate is significantly different from the layer structure at the joining area.
Further, in Patent Document 2, the difference between the heights of the joining areas due to the difference between the layer structures is compensated by filling a resin material or the like. However, the compensation may not be sufficient from the viewpoints of the bonding strength and the joining reliability between the supporting substrate and the fluid channel substrate. Therefore, when the deformation occurs such that the whole fluid channel substrate is bent, the effect of the crosstalk among the individual liquid chambers is enlarged. In addition, when the sufficient joining reliability between the supporting substrate and the fluid channel substrate is not ensured, a larger width of the joining area between the supporting substrate and the fluid channel substrate may be required. Consequently, the downsizing of the inkjet head may be difficult.